An answer to http://stackoverflow.com/questions/9777494

Makefile

CFLAGS = $(shell pkg-config --cflags mozjs185) -O2 -Wall
LDFLAGS = -Wl,--as-needed -Wl,-O1
LDLIBS = $(shell pkg-config --libs mozjs185)

all: parse
parse: parse.o
parse.o: parse.c date.js.h
date.js.h: date.js
	( \
		echo 'const char *code =' ; \
		sed -e 's/\\/\\\\/g; s/"/\\"/g; s/^/"/; s/\r\?$$/\\n"/' < $^; \
		echo ';' \
		) > $@
date.js:
	wget https://datejs.googlecode.com/files/date.js
clean:
	-rm date.js.h date.js parse parse.o

parse.c

#include "jsapi.h"
#include "date.js.h"

static JSClass global_class = { "global", JSCLASS_GLOBAL_FLAGS,
  JS_PropertyStub, JS_PropertyStub, JS_PropertyStub, JS_StrictPropertyStub,
  JS_EnumerateStub, JS_ResolveStub, JS_ConvertStub, JS_FinalizeStub,
  JSCLASS_NO_OPTIONAL_MEMBERS };

void reportError(JSContext *cx, const char *message, JSErrorReport *report) {
  fprintf(stderr, "%s:%u:%s\n",
      report->filename ? report->filename : "<no filename>",
      (unsigned int) report->lineno, message);
}

int main(int argc, const char *argv[]) {
  JSRuntime *rt;
  JSContext *cx;
  JSObject *global;
  rt = JS_NewRuntime(8L * 1024L * 1024L);
  if (rt == NULL) return 1;
  cx = JS_NewContext(rt, 8192);
  if (cx == NULL) return 1;
  JS_SetOptions(cx, JSOPTION_VAROBJFIX | JSOPTION_JIT | JSOPTION_METHODJIT);
  JS_SetVersion(cx, JSVERSION_LATEST);
  JS_SetErrorReporter(cx, reportError);
  global = JS_NewCompartmentAndGlobalObject(cx, &global_class, NULL);
  if (global == NULL) return 1;
  if (!JS_InitStandardClasses(cx, global)) return 1;

  /* Here's where the interesting stuff is starting to take place.
   * Begin by evaluating sources of date.js */

  jsval out;
  if (!JS_EvaluateScript(cx, global, code, strlen(code), "code", 1, &out))
    return 1;

  /* Now create a call to Date.parse and evaluate it. The return value should
   * be a timestamp of a given date. If no errors occur convert the timestamp
   * to a double and print it. */

  const int buflen = 1024;
  char parse[buflen + 1];
  snprintf(parse, buflen, "Date.parse(\"%s\").getTime();", argv[1]);

  if (!JS_EvaluateScript(cx, global, parse, strlen(parse), "parse", 1, &out))
    return 1;

  double val;
  JS_ValueToNumber(cx, out, &val);
  printf("%i\n", (int) (val / 1000));

  /* Finally, clean everything up. */

  JS_DestroyContext(cx);
  JS_DestroyRuntime(rt);
  JS_ShutDown();
  return 0;
}